a. Field of the Invention
The instant invention relates to electrical mapping of a patient's heart. In particular, the instant invention relates to a catheter which gathers data for high resolution cardiac mapping and associated components which generate a model showing a graphical representation of the heart and catheter even if portions of the catheter would otherwise be obstructed from view.
b. Background Art
A number of mapping and navigation options are available for electrical mapping of a patient's heart, for example, to navigate a catheter to a desired site within the patient's heart for an ablation or other medical procedure. For example, the EnSite NavX® utility is integrated into the Ensite® Advanced Mapping System (available from St. Jude Medical, Inc.), and provides non-fluoroscopic navigation of electrophysiology catheters.
The methodology implemented by this mapping system is based on the principle that when electrical current is applied across two surface electrodes, a voltage gradient is created along the axis between the electrodes. Although any suitable number of electrodes may be utilized, typically six surface electrodes are placed on the body of the patient and in three pairs: anterior to posterior, left to right lateral, and superior (neck) to inferior (left leg). The three electrode pairs form three orthogonal axes (X-Y-Z), with the patient's heart being at least generally at the center.
These six surface electrodes are connected to the Ensite® Advanced Mapping System, which alternately sends an electrical signal through each pair of surface electrodes to create a voltage gradient along each of the three axes, forming a transthoracic electrical field. Conventional electrophysiology catheters may be connected to the Ensite® Advanced Mapping System and advanced to the patient's heart. As a catheter enters the transthoracic field, each catheter electrode senses voltage, timed to the creation of the gradient along each axis. Using the sensed voltages compared to the voltage gradient on all three axes, the EnSite NavX® utility calculates the three-dimensional position of each catheter electrode. The calculated position for the various electrodes occurs simultaneously and repeats many times per second (e.g., about 93 times per second).
The Ensite® Advanced Mapping System displays the located electrodes as catheter bodies with real-time navigation. By tracking the position of the various catheters, the EnSite NavX® utility provides non-fluoroscopic navigation, mapping, and creation of chamber models that are highly detailed and that have very accurate geometries. In the latter regard, the physician sweeps an appropriate catheter electrode across the heart chamber to outline the structures by relaying the signals to the computer system that then generates the 3-D model. This 3-D model may be utilized for any appropriate purpose, for instance to help the physician guide an ablation catheter to a heart location where treatment is desired.
In order to generate an accurate and highly detailed map of a patient's heart, a large amount of data is required. Accordingly, an electrode catheter may be swept across various surfaces of the heart while obtaining data as described above. In order to accelerate this mapping data acquisition and/or increase the volume of data available for mapping, a number of high-density electrode catheters have been developed or proposed. Generally, these include a number of electrodes in an array in relation to a catheter body so as to substantially simultaneously obtain many mapping data points for a corresponding surface of cardiac tissue proximate to the catheter body. For example, these electrodes may be deployed along the length of a section of the catheter body that has a coil or other three-dimensional configuration so as to provide the desired spatial distribution of the electrodes. Alternatively, the electrodes may be disposed on a number of structural elements extending from a catheter body, e.g., in the form of a basket or a number of fingers.
Once the mapping data has been acquired, software may be implemented to generate multiple surface images, which when combined, comprise a three-dimensional image of the patient's heart. This image can be displayed on a suitable output device in real-time so that the physician can “see” the patient's heart and the catheter for properly positioning the catheter at a work site within the patient's heart for a medical procedure (e.g., an ablation procedure). However, the rendering techniques used to generate the three-dimensional image of the patient's heart necessarily result in portions of the catheter being obscured. For example, the catheter may be physically located “behind” the surface of the heart being viewed, and therefore portions of the catheter may be obscured from view in the rendered three-dimensional image. Or for example, the catheter may be drawn behind other objects being displayed for the physician, such as labels or other graphical entities.
By way of illustration, Ensite® Advanced Mapping System creates computer models of heart chambers which are then displayed graphically on the computer screen. Simultaneously, one or more catheters are also displayed in the corresponding position and orientation with respect to the heart chambers. Because the catheters are usually inside the heart chambers, the display of these catheters can be completely or partially obstructed (i.e., obscured from view) by the simultaneous or overlapping display of the heart chamber walls. The catheter can be additionally obscured from view by other graphical entities, such as labels, lesions, anatomical markers, and other catheters. Although the physician may have a good idea of where the catheter is within the heart, there exists a need to provide more clarity for the physician.